188 Proceedings of the Royal Physical Society. 



would necessarily assume a more or less uniform character. 

 Indeed, I suspect that much of the sediment of these early 

 seas may have been the result of tidal scour, and that 

 marine erosion was more generally effective than it is now. 

 With the gradual growth of the land and the consequent 

 deflection and limitation of current-action marine mechanical 

 sediments would tend to become more and more local in 

 character. Thus the increasing differentiation which we 

 observe in passing from the earlier to the later geological 

 systems is just what might have been expected. 



Summing up, now, the results of this rapid review of 

 the evidence, we seem justified in coming to the following 

 conclusions : — 



1st. In Palaeozoic times, Europe and !N"orth America were 

 represented by considerable areas of dry land, massed chiefly 

 in the higher latitudes, while further south groups of smaller 

 islands were scattered over the submero'ed surface of the 



o 



primeval continental plateau. The other continents appear, 

 in like manner, to have been represented by islands — some 

 of which may have reached continental dimensions. A very 

 remarkable uniformity of climate accompanied these peculiar 

 geographical conditions. 



2d. In Mesozoic times, the primeval continental plateau 

 came more and more to the surface, but the land-areas were 

 still much interrupted, so that currents from tropical regions 

 continued to have ready access to high latitudes. The 

 climate of the whole globe, therefore, was still uniform, but 

 apparently not so markedly so as in the preceding era. 



od. In Cainozoic times, the land-masses continued to 

 extend and the sea to retreat from hitherto submerged areas 

 of the continental plateau ; and this persistent land-growth 

 was accompanied by a gradual lowering of the temperature 

 of northern and temperate latitudes, and a more and more 

 marked differentiation of climate into zones. 



Having thus very briefly sketched the geographical evolu- 

 tion of the land during Pahieozoic, Mesozoic, and Tertiary 

 times, and come to the general conclusion that climate has 

 varied according to the relative position of land and 

 sea, I have next to consider the geographical and climatic 



